Google My Business : Target entire country

Google guidelines only allow you to set up GMB pages for businesses that either have a physical location that customers can visit, or that travel to visit customers where they are.

So, you can't set up GMB pages in every country that you want to service, unless you have a physical location there. You can set up brand pages through Google + or concentrate on building organic SEO for those locations.

For the home office where people do come as customers, you can set up a GMB listing.